Copolymer binders, e.g., butadiene/acrylonitrile, which contain carboxyl groups have been employed previously in photosensitive compositions. U.S. Pat. No. 3,825,430 to Kurka describes a light-sensitive composition containing a continuous phase of a light-sensitive organic material and a discontinuous phase of a finely divided, elastomeric organic compound uniformly distributed through the continuous phase, e.g., a carboxyl-containing, high molecular weight butadiene/acrylonitrile copolymer. The discontinuous phase generally represents 5-50% by weight of the total composition.
Canadian Patent No. 614,181 to McGraw describes a photopolymerizable composition comprising at least 40% by weight of a butadiene homopolymer or copolymer binder including butadiene/acrylonitrile and butadiene/methacrylic acid copolymers, at least 10% by weight of an addition-polymerizable ethylenically unsaturated compound and 0.001 to 10% by weight of polymerization initiator.
U.S. Pat. No. 4,177,074 discloses photosensitive, elastomeric compositions containing (1) a high molecular weight butadiene/acrylonitrile copolymer which preferably contains carboxyl groups, (2) a low molecular weight butadiene polymer, (3) an ethylenically unsaturated monomer, and (4) a free-radical generating system. The compositions have outstanding properties as photosensitive coatings for flexographic printing plates.
German Patent Specification No. 2,720,228 to Japan Synthetic Rubber Company, published Dec. 1, 1977, discloses photosensitive compositions consisting of (I) a copolymer of (a) a conjugated diene, (b) an .alpha.,.beta.-ethylenically unsaturated carboxylic acid or anhydride, and optionally (c) a monoolefinically-unsaturated compound, e.g., a butadiene/acrylonitrile copolymer; (II) a photosensitizer and/or light-sensitive cross-linking agent; and (III) a photopolymerizable unsaturated monomer, useful for flexographic relief printing plates. The carboxyl groups of the copolymer may be neutralized with an alkali metal cation or amine cation. Such neutralized compositions are readily developable in water after exposure to radiation. No specific examples of a neutralized carboxyl-containing butadiene/acrylonitrile copolymer are employed, and neutralization with a Group IIA or IIB metal cation is not disclosed.
U.S. Pat. No. 3,787,212 to Heimsch et al describes photosensitive compositions containing an acrylonitrile/diene interpolymer and an aromatic ketone sensitizer for use in photoresist applications. There is no disclosure in Heimsch et al of a composition useful for the manufacture of flexographic printing plates which contain as the binder a carboxylated high molecular weight butadiene/acrylonitrile copolymer in which some or all of the carboxylic acid protons are exchanged for metal ions of Group IIA or IIB.
U.S. Pat. No. 3,016,297 to Mochel et al describes cross-linking of photopolymerizable compositions via chelation with a polyvalent metal, usually employing electron donor groups located 1,3 with respect to one another along a polymer chain. Carboxyl-containing butadiene/acrylonitrile copolymer binders are not disclosed and no specific examples are given which illustrate use of a carboxyl electron donor group.
Cross-linking of carboxyl-containing butadiene elastomers with metal ions of Groups 1-3 of the Periodic Table to give thermally reversible cross-links is reviewed by Brown in Rubber Chem. Tech., 36, p. 931-962 (1963); see also British Patent No. 1,179,252 to Locke and Hawkins which discloses cross-linking polymers containing carboxyl groups by a thermally reversible process using metal ions of Groups 1-3.